The overall objective of this research project is to achieve a better understanding of the mechanisms of arrhythmias causing sudden cardiac death by tackling the ionic and cellular mechanisms of early (EADs) and delayed (DADs) after depolarizations. EADs are classically attributed to reactivation of the L-type Ca current or to spontaneous sarcoplasmic reticulum (SR) Ca release (i.e. SR Ca release not directly gated by the L-type Ca current) in the setting of reduced repolarization reserve. DADs are attributed to spontaneous SR Ca release in the form of Ca waves stimulating Ca-sensitive inward currents such as Na-Ca exchange. Recently, we have presented evidence for a mechanism (chaos synchronization) by which EADs simultaneously create triggers and enhance tissue substrate vulnerability to promote lethal arrhythmias. A comparable theory does not yet exist, but is being developed, for DADs. The goals of this project are: i) to explore the cellular basis of EADs that set the process of chaos synchronization in motion;ii) to test whether theoretically-predicted rotors mediated by the L-type Ca current (related to the biexcitability of cardiac tissue) can be detected experimentally in cardiac tissue as a mechanism of Torsades de pointes;iii) to explore the cellular basis of DADs, specifically how the microscopic behavior of Ca release units in the sub cellular Ca cycling network integrates to generate Ca alternans, Ca waves, DADs and EADs at the whole cell level;iii) to explore the interactions between EADs and DADs that together generate triggers and modify substrate by increasing tissue electrical dispersion predisposing to VF. To accomplish these goals, we will combine patch clamp (including a dynamic patch clamp technique) and fluorescent dye studies at the cellular level with optical mapping studies at the tissue level. Improved understanding of the cellular mechanisms of after depolarizations which cause lethal arrhythmias is essential for developing novel therapy. PUBLIC HEALTH RELEVANCE: The proposed research will study the mechanisms of sudden cardiac death due to ventricular arrhythmias, which prematurely takes the lives of more than 300,000 U.S. citizens each year. The goal is to use this information to develop novel therapies to prevent this deadly manifestation of heart disease.